1. Field of the Invention
This invention relates to the field of phase encoded pattern recognition and the use of digital techniques to perform spectral analysis on phase encoded signals.
2. Background Art
Communication of data information on the voice network between a sending and receiving station is typically accomplished with a modem (modulator/demodulator). A modem transforms digital information by modulating it according to a well known modulating scheme. This modulated data is transmitted to a receiving modem, where it is demodulated to produce the original information. During the transmission of data from a transmitting modem to a receiving modem, a series of phase encoded tones are utilized to provide set up information to the modems. These tone sequences represent data patterns and are known as "hand shake" sequences. One particular hand shake sequence is known as the V.22 bis modem handshake sequence. In order to receive the hand shake signals,it is necessary to acquire, detect and decode the hand shake sequence. The hand shake sequence typically consists of phase encoded information.
In the prior art, a coherent, or clock recovered, detection scheme is utilized. These prior art detection schemes suffer from the time required to acquire the large dynamic range found during the hand shake sequence. In addition, prior art detection schemes are dependant on the particular modulation technique utilized and are therefore algorithm dependant. Further, prior art coherent pattern detection schemes, because they are dependant on the modulation technique, so not operate effectively or quickly in a noisey environment. Thus, coherent detection requires a large amount of code to detect the various signals. In addition, the coherent technique requires more time to require the desired pattern.
Therefore, it is an object of the present invention to provide a fast method for pattern detection.
It is another object of the present invention to provide a method of pattern detection which is not hardware or firmware intensive.
It is yet another object of the present invention to provide a method of recovery which does not require a data clock.